Sustainable Safe Water Devices

Deep Tube Well (DTW)

The DTW is one of the most popular devices for drinking water in Bangladesh. A hand pump is used to extract groundwater from it.

Water Source: Confined aquifer in between 120-300m depth.

Drilling Method: Donkey Pump

Gravel Packing and Cement Sealing:

After inserting the sand trap, strainer and total pipe; the annular space between the pipe and borehole is filled up with gravel up to the aquitard layer (top of the targeted aquifer). Then cement sealing is carried out to protect arsenic contamination from first aquifer.

Note: Cement Sealing

  1. What is Cement Sealing?
    • To seal any opening using cementing materials is called Cement Sealing.
  2. What is Deep Tube Well Cement Sealing?
    • Deep Tube Well Cement Sealing is a method by which vertical propagation of arsenic and other hazardous materials from shallow aquifer (first aquifer) to deep aquifer (second aquifer) is protected.
  3. Why it is necessary?
    • When a deep tube well is installed, an annular space is created around the pipe. It creates the possibility of passing water from the shallow contaminated aquifer to deep uncontaminated aquifer by vertical propagation. As a result, deep aquifer slowly and gradually becomes contaminated. To stop this contamination we need to create obstacle by cement sealing up to a certain depth (~100m) around the pipe. Otherwise, one by one deep aquifer of the total area gets contaminated with arsenic and other toxic materials.
  4. What is the basic issue we have got to consider before cement sealing?
    • There should a considerable clay/silty clay/silt layer (6m for clay/9 for silt) between the first and second aquifers.
Photo: Cement Sealing

Drainage System: A drainage system is constructed surrounding the GI (galvanizing Iron) pipe to stabilize the pump and to maintain the hygienic condition.

Maintenance: The maintenance of DTW is very simple compared to other devices. Hand pump maintenance is the main task. The operation and maintenance of DTW is described below:

Materials Requirement: Gaston, Iron brush, pipe, screwdriver, plush, scissors, tape, wrench, etc.

Daily Maintenance: Every morning, the surrounding should be kept clean.

Weekly Maintenance:

  1. Clean the leaf and wastage near the platform and drain. If cleaning is not properly done, it may create unhygienic condition near the platform.
    • Clean the algae substance from the platform by the iron brush. It may create accident at the time of water taking

Monthly Maintenance:

  1. Wipe up useless plant/weed near the platform. It may create jangles near the DTW.
  2. Put oil or grease if necessary or replace the inactive parts. If oil or grease are not used, the hand pump parts may be damaged or broken easily. Excess oil or grease may contaminate water of the DTW.
  3. Cover in the furrow between platforms and the underlying ground by mud, otherwise the platform may be broken being fractured.

Pond Sand Filter (PSF)

PSF is a community based filtration system that purifies pond water for drinking purpose.

Water Source: Pond water.

Filtration System: Up-flow, down-flow and horizontal roughing systems

Design of the Filtration Units: The filtration units consist of raw water chamber, roughing chamber, slow sand chamber, and clear water chamber.

Filter Media:

  • Rounded gravels of 4 sizes
    1. 5-8mm
    2. 8-12mm
    3. 12-15mm
    4. 15-20mm
  • Sand (1.2-2.5FM)

Drainage System: A drainage system with inspection pit is constructed surrounding the structure to maintain the hygienic condition.

Maintenance:

  • Daily maintenance
  1. Clean the leaf and wastage from the platform, filter roof, the drainage and surrounding areas.
  2. Ensure chlorination of the filtered water by adding bleaching powder from morning to evening
  • Weekly Maintenance
  1. Open the drainage-valve of gravel and sand filters until clean water comes out.
  2. Clean excess or died algae from the slow sand filter’s tank.
  3. Clean the substance, leaf or wastage found in the pond and around the inlet screen pipe in case of PSF.
  4. Remove the calcium carbonate crystal (white/brown) from the gravel, slow sand filter and supply tanks (DWSF & AIRP).
  • Monthly Maintenance
  1. Scrape 1-2 cm of the slow sand filter’s top sand to remove sludge. Scraped sand can be reused after proper washing.
  2. Put oil or grease if necessary or replace the inactive parts. If oil or grease is not applied, then the hand pump parts may be damaged or broken easily.
  3. Wipe out unnecessary plant/weed near filter sites.
  4. Clean any things that fall into the pond or inside the dug well (PSF and DWSF).
  5. Cover the open space between platform and underlying ground by mud.
  • Half Yearly Maintenance
  1. If necessary, remove all the gravels from the gravel chambers, and wash it properly by water. Clean the inside walls of all chambers with brush and bleaching powder. In case of AIRP, sand of slow sand filter must be washed.
  2. Paint the iron/steel parts.
  •  Yearly Maintenance:
  1. Add new sand in the slow sand chamber, to maintain 0.8m thickness.
  2. Repair embankment if damaged.
  3. Re-excavate the dug well. If the dug well depth is 2 feet shorter than the original, then take necessary steps to re-excavate the dug well. (DWSF).
  • Long-term Maintenance:
  1. Pond should be re-excavated at every 10 years to preserve enough water. (PSF)
  2. Slow sand chamber’s sand should be replaced, if it is seen that even after washing the sand, the performance of arsenic removal is decreased.

Dug Well Sand Filter (DWSF)

DWSF is a community based filtration system that purifies dug well (Indara) water for drinking purpose. This dug well was the main device of drinking water in the rural areas of Bangladesh. For the first time in Bangladesh, we attached a filtration system with dug well to safeguard bacteriological contamination and other hazardous elements (e.g., arsenic, manganese, ammonium, etc).

Water Source: Sub-surface groundwater usually at a depth of 10m or less.

Filtration System: Up-flow, down-flow and horizontal roughing systems

Design of the Filtration Units: The filtration units consist of raw water chamber, roughing chamber, slow sand chamber, and clear water chamber.

Filter Media:

  • Rounded gravels
    1. 5-8mm
    2. 8-12mm
    3. 12-15mm
    4. 15-20mm
  • Sand (1.2-2.5FM)

Drainage System: A drainage system with inspection pit is constructed surrounding the structure to maintain the hygienic condition.

Maintenance: See PSF Maintenance section

Arsenic Iron Removal Plant (AIRP)

AIRP is a water treatment plant that uses the principle of co-precipitation of arsenic and iron through aeration and filtration. For treating water, special attention is given to the raw water quality. The presence of arsenic, iron and phosphate should be properly judged for effective treatment. We usually select water with arsenic less than 150µg/L. If the water contains phosphate significantly, the acceptable limit of arsenic contaminated water should be 100µg/L or less.

Water Source: Shallow or existing deep tube well.

Filtration System: Aeration channel and tray, up-flow and horizontal roughing systems

Design of the Filtration Units: The filtration units consist of raw water chamber, roughing chamber, slow sand chamber, and clear water chamber. Aeration tray is place just over the inlet and the channel is filled with rounded gravels to facilitate air mixing with water.

Filter Media:

  • Rounded gravels
    1. 5-8mm
    2. 8-12mm
    3. 12-15mm
    4. 15-20mm
  • Sand (1.2-2.5FM)

Maintenance: For maintenance, it is needed to clean the aeration channel monthly to maintain water flow and to prevent entrance of sludge inside the raw water chamber. The sludge which is deposited in the sludge pit, is dumped in a safe place (usually, in brickyard).

For other types of maintenance, please see PSF Maintenance section.

Pipe Water Supply System (PWSS)

PWSS is a sustainable water treatment system which purifies water of a large perennial source (e.g., ox-bow-lake, deep aquifer, river, etc). Our organization only treats surface water from ox-bow-lake.

Filtration System: Up-flow

Design of the Filtration Units: The filtration units consist of raw water chamber, roughing chamber, slow sand chamber, clear water chamber, overhead tank and distribution pipeline network.

Filter Media:

  • Rounded gravels
    1. 5-8mm
    2. 8-12mm
    3. 12-15mm
    4. 15-20mm
  • Sand (1.2-2.5FM)

Mechanism of Filtration Unit:

Lake water is first pumped up into a raw water tank and then it flows down into the filtration units. The filtration units consist of three gravel chambers and one sand chamber. On the top of the sand beds, algae and aquatic organisms are born. Inside the sand bed, many insects and micro-organisms live. They consume organic matters, microbes and chemicals that are harmful for health. Hence, the system is called a “biological filtration system”. After filtration, chlorine is added to prevent any microbial contamination that poses potential risk for human health.

This purified water is pumped up into an overhead tank and is supplied to the door-step of the people through a pipeline network.

Drainage System: A drainage system is constructed surrounding the structure to maintain the hygienic condition.

Maintenance System: Surrounding areas are cleaned on a regular basis. Get-valves of all washout pipes are opened for about 2 minutes as a weekly maintenance. Once in a month, the slow sand filtration bed is scrapped out (5-10mm) for removing dead algae, the pre-filter bed (gravel chamber) is washed for removing turbid materials and the washout of distribution pipeline is opened for about 5 minutes for cleaning accumulated sediments. When discharge rate gets slower, the sand used in the slow sand filter is completely changed or reused after proper washing. The area around the tap point is usually maintained by the tap committee. If there is any big technical fault, the user committee asked for external help.

Rainwater Harvesting System (RHS)

RHS is way to collect rainwater in a big tank using rooftop. A tin or concrete roof is ideal for rainwater harvesting. After getting cleaned the rooftop by the first few minutes of shower, the water is allowed to go inside the tank. The water is collected through a gutter/flexible pipe. The habit of consuming rainwater is not new for Bangladesh – in some areas of costal belt it is being traditionally used. This water is arsenic-safe and potable in principle. It should be cleaned and disinfected by bleaching powder twice in a year – just before the rainy season starts and just before the rainy season ends.

In case of Bangladesh, it usually provides water for about 8~10 months depending on rainfall. During the dry season, when water storage is not enough, it is difficult to meet the needs of the users.

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